1. Technical Field
Aspects of the example implementations relate to an improved X-ray collimator for controlling a radiation field shape when radiated X-rays are partially blocked to irradiate an affected area with therapeutic X-rays.
2. Related Art
In radiation (X-ray) therapy, a device such as a multileaf collimator is used for controlling a radiation field so as to make a radiated X-ray substantially coincide with the shape of an affected area. This multileaf collimator is composed of a combination of plate-like members, which are referred to as leaves, and rectangular in planar view with a heavy metal (tungsten, lead, etc.) as a material. The respective leaves constituting the multileaf collimator are intended to be independently subjected to movement control in the longitudinal directions of the leaves by an electrical driving source, so as to make the radiation field of therapeutic beams coincide with the shape of an affected area (for example, see Japanese Patent Application Laid-Open No. 2010-240085 (pp. 3-4, FIG. 2)). However, because the respective leaves constituting the multileaf collimator are rectangular in planar shape, the aperture shape of the leaves is a combination of linear shapes, and the shape of the radiation field is also defined by the linear shapes. Therefore, in order to apply radiation therapy to complex three-dimensional shapes such as tumors without causing damage to surrounding healthy tissues, there is room to improve the accuracy of forming the radiation field.
Accordingly, aperture diaphragms for collimating radiation have been proposed. For example, a mechanism for forming an iris aperture from six triangular leaves obtained by dividing a hexagon into six equal parts has been proposed, and this mechanism can change the minimum circular opening aperture from the minimum hexagonal opening to the maximum by use of the six triangular leaves (for example, see Japanese Patent Application Laid-Open No. 2008-536654). In addition, an apparatus has also been proposed which can change an aperture shape for transmitting X-rays between a circle with a first diameter and a circle with a second diameter by combining six blades for shielding X-rays and rotating rotation axes provided for each of the respective blades (for example, see Japanese Patent Application Laid-Open No. H09-512641). Furthermore, an apparatus has also been proposed which has a mechanism including four to six aperture blades and moving all of the aperture blades by the same adjustment stroke at the same time for forming an opening (aperture) using parts of the aperture blades (for example, see Japanese Patent Application Laid-Open No. 2008-539833).
However, the above-described collimators for adjusting the sizes of the apertures merely narrow the opening to circular or polygonal shapes to define the radiation fields for affected areas into circular shapes or polygonal shapes. Thus, since many affected areas are typically present in elongated shapes, there is a need for X-ray irradiation more than once in those cases. Therefore, there are problems such as the increased burden on patients, and radiation therapy has been desired which is completed with a minimum number of exposures.